Our finding that 3,6-dideoxydihydromorphine had antinociceptive activity equivalent to morphine and that, in the rhesus monkey, its pharmacological actions also paralleled those of morphine (e.g.-physical dependence liability), led us to study the metabolism of the compound. It was, a prior, possible that the compound could be hydroxylated in vivo and the resultant phenolic compound could be responsible for the observed pharmacological effects. The study has shown, thus far, that 3,6-dideoxydihydromorphine is not metabolized to a phenolic compounds. Thus, contrary to previous assertions in the literature, the phenolic hydroxyl group in opioids is not essential for either antinociception or physical dependence.